Method of adapting finned tubing for joining



' April 2-8, 1970 D. L. HILL ETAL 3,508,508

METHOD OF ADAPTING FINNED TUBING FOR JOINING 2 Sheets-Sheet 1 Filed Feb.26, 1968 fIG-S INVENTOR. DW/GHT L HILL RICHARD 14.5H/VE ATTORNEY April28, 1970 D.L. ETAL 3,508,508

METHOD OF ADAPTINQ FINNED TUBING FOR JOINING Filed Feb. 26, 1968 '2Sheets-Sheet 2 INVENTOR I DWIGHT L. H/LL RICHARD A. SH/VE ATTORNEYUnited States Patent U.S. Cl. 113-118 9 Claims ABSTRACT OF THEDISCLOSURE Providing finned tubing having fins integral therewith,severing at least one fin substantially inward towards the tube portion,and then deflecting the fins sufliciently inward towards said tubeportion to provide an overlay in contacting arrangement and contiguouswith the external surface of the tube portion.

Finned tubing has found extensive and long use in a Wide variety ofapplications wherever a high rate of heat transfer is required. Thefins, being bonded to the tubing, provide a large increase in effectivesurface area and thus correspondingly increase the rate of heat transferbetween the medium passing through the finned tubing and the medium onthe outside of the tubing.

For example, finned tubing is used extensively in heat exchangerapplications wherein condensing, e.g. steam to water, is required. Themedium passing through the tubing, being employed at a substantiallylower temperature than that being condensed, maintains a largelyincreased condensing surface at a temperature lower than the temperatureof the outside medium and thus provides for increased condensation.Conversely, the cooling medium, rather than passing through the finnedtubing, may be employed on the outside with the medium being condensedpassing through the inside.

Naturally, finned tubing is not limited to applications wherein acondensing action is required, but rather the application of finnedtubing includes heat transfer, or the exchange of heat, when the mediumon both sides of the tubing are liquid, or both gaseous, or acombination thereof. Condensation per se may or may not be requireddepending upon the particular application contemplated.

Pinned tubing when employed in a particular heat exchanger may be fittedto material, such as heavier Walled conventional tubing, ie, withoutfins, Method of joining include, e.g. welding, brazing, mechanicalconnecting, and employing an adhesive in combination with mechanicalconnecting. Connections in combination with the use of adhesives are notespecially critical and include all phases of lap type joining adaptableto tubing.

Mechanical joining of finned tubing to conventional tubing having agreater wall thickness, however, provides a joint of substantially lessmechanical strength than if the finned tubing were of more nearly thesame wall thickness since the finned tubing necessarily contributes alesser amount of metal to the joint than the conventional tubing.

Likewise the difference in wall thickness will, upon cooling afterwelding, cause an uneven stress pattern to occur at the area of thejoint since the cooling rates are necessarily dissimilar and thus alsocause a reduction in mechanical strength of the joint.

Thus, it is a particular object of the present invention to provide amethod of preparing finned tubing for joining to conventional tubing ofa greater wall thickness, and the article produced thereby.

It is an additional object of the present invention to provide a methodfor increasing the mechanical strength of the joint between the finnedand conventional tubing ice by increasing the wall thickness and toprovide an area of the finned tubing more readily adaptable to variousmethods of joining.

It is a further object of the present invention to provide a process andarticle aforesaid while retaining the highly desirably characteristicsof finned tubing.

It is a still further object of the present invention to provide asimple and expeditious process which accomplishes the aforesaid objectsconveniently and at a commercially competitive cost.

Further objects and advantages of the present invention are apparenthereinafter.

FIGURE 1 is a partial perspective view of one end of a finned tubing;

FIGURE 2 is a partial perspective view of one end of a finned tubingshowing fins severed at a right angle to the tube portion;

FIGURE 3 is a partial perspective view of one end of a finned tubeshowing that portion of the fin severed from the remainder of said finfolded longitudinally and downwardly towards the tube portion;

FIGURE 4 is a partial perspective view of one end of a finned tubingshowing the folding of FIGURE 3 completed;

FIGURES 5-8 are partial perspective views of alternative embodiments ofsevering the fin substantially inward towards the tube portion;

FIGURE 9 is a partial perspective view of one end of a finned tubingshowing folding of unsevered fins longitudinally and downwardly towardsthe tube portion.

Briefly, the process of the present invention comprises, providing afinned tubing having fins integral therewith, severing at least one finsubstantially inward towards the tube portion, and then deflecting thefins sufficiently inward towards said tube portion to provide an overlayin contacting arrangement and contiguous with the external surface ofthe tube portion.

Preferably, the attached fins should be of sufficient outwardlyextending length so that the external surface of the tube portion willbe substantially covered after deflecting to form the overlay.Naturally, the total outwardly extending length of the attached fins mayexceed the circumfeience of the tube portion so that successive overlaysmay be built up.

Normally, fin tubing comprises a plurality of integral fins, althoughonly one attached fin would be necessary if the outwardly extendinglength thereof at least substantially equalled the circumference of thetube portion.

Referring to the drawings, FIGURE 1 shows an end portion of aconventional finned tubing, with fins 1 and 2 being aflixed to tubeportion 3.

FIGURE 2 shows fins 1 and 2 severed inward substantially to tube portion3 forming separate portions 4 and 5 of each fin substantially freed fromthe remainder of the fins.

FIGURE 3 shows initial deflection of the freed fin portions and FIGURE 4shows deflection completed thereby forming a terminal overlay of saiddeflected fin portions in contacting arrangement and substantiallycontiguous to the external surface of the tube portion 3. Thus, as shownin FIGURE 4 the arrangement of overlay 6 is readily adaptable to variousmethods of joining with conventional tubing having a greater wallthickness than that of the finned tubing. In effect, the Wall of thefinned tube has been doubled in thickness thereby providing additionalmetal for increased mechanical strength of a subsequent joint toconventional tubing.

If desired, severed fin portions 4 and 5 may be metallurgically bondedto tube portion 3. For example, a bonding agent comprising a lowermelting material than that of the severed fin or tube portions may besuitably placed between the inside suiface of the severed fin portions 4and 5, comprising overlay 6 and the external surface of tube 3 and theentire assembly heated sufliciently to cause a metallurgical bond. Anyconvenient method of introducing the bonding agent may be employed, suchas coating the external surface of tube portion 3 before deflectingsevered fin portions 4 and 5, or coating those surfaces of severed finportions 4 and to be substantially contiguous with tube portion 3. Afterdeflection of fin portions 4 and 5, the bonding agent is then incontacting arrangement with overlay 6 and tube portion 5, and theassembly is then ready for heating. Preferably external pressure isapplied to the assembly during the heating step to insure continuedintimate contact of overlay 6, the bonding agent, and tube portion 3thereby insuring proper metallurgical bonding.

Metallurgical bonding may be accomplished in other ways, as for example,by pre-heating a die in which severed fin portions 3 and 4 are deflectedand contacted with tube portion 3. The combination of heat given up tothe assembly and pressure in forming the overlay will provide propermetallurgical bonding.

The method of severing fins 1 and 2 to form severed portions 4 and 5 isnot critical and any convenient method such as cutting, blanking,stamping, sawing, etching, etc. may be employed.

Likewise, the method of deflecting severed fin portions 4 and 5 is notcritical and methods such as hand working, sawing, rolling, drawing,wiping, forging, vacuum form'- ing, etc. are readily adaptable to thepresent invention.

If desired, fins 1 and 2 may be deflected to form overlay 6 around atleast one end of tube portion 3 without the aforementioned severingoperation to form severed fin portions 3 and 4 and the same basicmethods of deflection, as aforementioned, are equally adaptable. By thisembodiment additional metal is also provided for increased jointstrength, regardless of the method of forming the joint. If desired,overlay 6 may also be metallurgically bonded to tube portion 3 asaforementioned.

Pinned tubing prepared in accordance with the present invention isreadily adaptable to joining to conventional tubing without fins, usingconventional methods of joining, as well as to additional finned tubingalso prepared in accordance with this invention.

If so desired, both ends of finned tubing may be prepared in accordancewith the present invention.

For example, the present invention is readily adaptable to various typesof connections employing adhesives. Various connections include inserttype connections as well as all types of lap type joining adaptabletotubing such as for example, simple, lap, joggle lap, tapered lap, etc.Suitable adhesives include epoxies, pipe joint cement, rubber basedcement, etc.

Mechanical compression fittings may also be employed withoutencountering the problems attendant with tubing of lesser wall thicknessi.e. the increase in effective wall thickness provides the increasedmechanical strength requisite for this type of fitting.

Depending upon the relative inside diameter, or bore, of the tubing tobe joined, one may be inserted into the other for a suitable distanceand then joined in this position. Suitable adhesives, as aforementioned,are also especially useful in this method of joining.

The present invention is also readily adaptable to welding for forming ahigh strength bond. Heliarc welding, in particular, may preferably beemployed due to the increased amount of available metal of overlay 6.

Thus, it may be seen that the present invention provides a simple andexpeditious method for preparing finned tubing for joining toconventional tubing of thicker wall diameter whereby increasedmechanical strength of 4 the joint is obtained while maintaining thehighly desirable characteristics of finned tubing.

The fin portions may be severed as aforementioned before forming theoverlay, or may be formed into the overlay without severing and, ifdesired, a bonding agent comprising a lower melting material may beemployed in order to metallurgically bond the overlay formed with thetube portion.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiments are therefore to be considered as inall respects illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, and all changes whichcome within the meaning and range of equivalency are intended to beembraced therein.

What is claimed is:

1. A method of adapting finned tubing for joining to material of greaterwall thickness comprising:

(A) providing a heat exchange element comprising a tube, and at leastone outwardly extending fin integral therewith, with the total outwardlyextending fin length being at least substantially equal to thecircumference of said tube; and

(B) deflecting at least one portion of said fin sufliciently inwardtowards said tube to provide an overlay of said fin in contactingarrangement and substantially contiguous with the external surface ofsaid tube.

2. The method of claim 1, wherein said fin at one end of said tube isdeflected sufficiently inward towards one end of said tube to provide anoverlay of said fin in contacting arrangement and contiguous with saidexternal surface of said one end of said tube.

3. The method of claim 1, wherein there are two said fins ofsubstantially equal outwardly extending length.

4. The method of claim 1, further providing the step of substantiallysevering at least one said fin inwardly towards said tube to provide aterminal end portion of said fin before deflecting said fin to form saidoverlay.

5. The method of claim 3, further providing the step of substantiallysevering at least one of said fins inwardly towards said tube to providea terminal end portion of said fin before deflecting said fins to formsaid overlay.

6. The method of claim 5, wherein said fins have a total outwardlyextending fin length substantially equal to the circumference of saidtube.

7. The method of claim 3, wherein said fins have a total outwardlyextending fin length substantially equal to the circumference of saidtube.

8. The method of claim 1, further including the step of metallurgicallybonding said overlay to said tube.

9. The method of claim 7, further including the step of metallurgicallybonding said overlay to said tube.

References Cited UNITED STATES PATENTS 2,236,185 3/1941 Murray29--15'7.3 X 2,578,305 12/1951 Huet 183 X 2,780,000 2/1957 Huet 723672,963,779 12/1960 Mosgard-Jensen 29157.3 2,978,797 4/1961 Ekelund29-1573 CHARLIE T. MOON, Primary Examiner D. C. REILEY, AssistantExaminer US. Cl. X.R.

